I have written a book on the politics of autism policy. Building on this research, this blog offers insights, analysis, and facts about recent events. If you have advice, tips, or comments, please get in touch with me at jpitney@cmc.edu

But is there any room left for an actual increase in the prevalence of ASD?

Potentially. For example, researchers have also found associations between both the mother’s and father’s age and risk for ASD — that is, the older the parents, the greater the chance of having a child with ASD. And women in the U.S. are having children later today compared to 2000, according to the CDC. However, we couldn’t find similar data on U.S. men. We also couldn’t find a study that quantified how much increasing parental ages could be contributing to increased prevalence of ASD in the U.S.

If Trump had said that there has been a “tremendous” increase in the number of reported cases of ASD, that would be true.

But it’s unclear, at best, that there’s been a “tremendous” increase in the actual number of children who exhibit ASD’s symptoms.

Research suggests that broadened diagnostic criteria, greater awareness and diagnostic recategorization of ASD with similar disorders may account for a portion, if not the majority, of this reported increase.

Currently, the CDC says the “increase in ASD diagnosis is likely due to a combination” of the these factors and an actual increase.

What is clear, however, is that there is no evidence to support any contribution by vaccines to the increase in reported prevalence of ASD, as Trump implied back in 2015.

But vaccines are under threat from a political source: US president Donald Trump is raising doubts about the safety and value of vaccines. Last week, immunologist Prof Kingston Mills of Trinity College Dublin spoke of the “Trump effect”, as the newly installed president spreads fear about vaccine safety over social media.

“President Trump has been tweeting about vaccines, making claims about links with autism,” Prof Mills said. “He has been adding further fuel to the fire that vaccines have side-effects that have not been proven.” Among the 20 vaccines that prevent life-threatening diseases are immunisations against deadly strains of meningitis, the congenital damage caused by rubella in expectant mothers, and the cancer-causing human papillomavirus (HPV).

HPV vaccine has the potential to reduce deaths from cervical cancer; however the uptake of the vaccine in the Republic has dropped to 50 per cent due to a campaign claiming it caused chronic fatigue syndrome. And while the putative link has not been proven, the negative publicity persists.

It is no coincidence Trump’s election campaign featured the disgraced doctor Andrew Wakefield, who was struck off the medical register in Britain after fraudulently claiming the MMR vaccine caused autism. The actor Robert de Niro and prominent campaigner Robert J Kennedy have called for a vaccine commission to be established. “Anti -vaxxers” are close to power in the US and could do untold damage to global health.